1. Field of the Invention
The invention relates in general to handrail apparatus, and more specifically to handrail apparatus for a transportation system, such as an escalator, which includes a continuous, flexible handrail member which is both pushed and pulled about a substantially continuous guide loop.
2. Description of the Prior Art
U.S. Pat. No. 3,712,447, which is assigned to the same assignee as the present application, discloses a handrail guide system for passenger conveyors, such as escalators and movable walks, which permits the handrail to be both pushed and pulled about a substantially continuous guide loop. This arrangement has many advantages over apparatus which obtains the tractive force necessary to propel the handrail member by only pulling it around a discontinuous guide loop. The latter arrangement develops a relatively large tension in the handrail member, causing it to wear and stretch. In the hereinbefore mentioned U.S. patent, the length of the guide loop is initially adjusted to the length of the handrail loop.
U.S. Pat. No. 4,239,102 improves upon the handrail guide system of U.S. Pat. No. 3,712,447 by disclosing a guide loop is a push-pull system which automatically adjusts its length in response to changes in the loop length of the handrail member. In this patent, a flexible portion of the guide loop is cut, and the cut ends are linked by a biasing arrangement which biases the cut ends away from one another. The guide loop length is initially adjusted via a manually adjustable take-up, such that a predetermined gap is produced between the cut ends of the flexible portion of the guide loop, enabling the loop length of the handrail to increase, or decrease, over a predetermined adjustment range. The biasing means is selected to create a very slight tension in the handrail over the entire adjustment range.
The push-pull handrail system has certain disadvantages when subjected to a load by passengers on the transportation apparatus. The load induced forces cause the handrail to press against the handrail guide, especially adjacent the curved ends of the guide loop, causing undue wear of the handrail and guide member. The problem becomes even more acute when the push-pull handrail system is applied to rises higher than about 20 feet. The modular type of escalator drive disclosed in U.S. Pat. Nos. 3,677,388 and 3,707,220, makes almost any rise practical, as only one type of standard drive is used regardless of rise. Additional drives are simply added to the inclined portion of the truss to accommodate any particular rise. Each such drive includes a handrail drive. A single drive is used for rises up to about 20 feet. With a single drive, excess passenger load on the handrail will usually cause slippage at the handrail drive interface. While such slippage mars the appearance of the handrail, and reduces its useful life due to accelerated wear, the slippage limits the handrail-guide forces to the point where the handrail will usually stay on the guide. When more than one drive is used, however, the driving forces are so great it is difficult to cause the handrail to slip in the drives. Thus, load induced forces become so great that the handrail may pop off the guide. A prior art approach to preventing the handrail from being forced from its guide uses a plurality of rollers which are spaced between the uppermost drive of the modular drive arrangement and the uppermost newel of the balustrade. Each roller is positioned immediately below the handrail in this area, to limit the movement of the handrail in the downward direction, i.e., the direction which can cause the handrail to pop off the guide.